A novel indirect defence in Brassicaceae: Structure and function of extrafloral nectaries in Brassica juncea

While nectaries are commonly found in flowers, some plants also form extrafloral nectaries on stems or leaves. For the first time in the family Brassicaceae, here we report extrafloral nectaries in Brassica juncea. The extrafloral nectar (EFN) was secreted from previously amorphic sites on stems, flowering stalks and leaf axils from the onset of flowering until silique formation. Transverse sections at the point of nectar secretion revealed a pocket‐like structure whose opening was surrounded by modified stomatal guard cells. The EFN droplets were viscous and up to 50% of the total weight was sugars, 97% of which was sucrose in the five varieties of B. juncea examined. Threonine, glutamine, arginine and glutamate were the most abundant amino acids. EFN droplets also contained glucosinolates, mainly gluconapin and sinigrin. Nectar secretion was increased when the plants were damaged by chewing above‐ and belowground herbivores and sap‐sucking aphids. Parasitoids of each herbivore species were tested for their preference, of which three parasitoids preferred EFN and sucrose solutions over water. Moreover, the survival and fecundity of parasitoids were positively affected by feeding on EFN. We conclude that EFN production in B. juncea may contribute to the indirect defence of this plant species.     

Animal and vegetation patterns in natural and man-made bog pools: implications for restoration

1. Peatlands have suffered great losses following drainage for agriculture, forestry, urbanisation, or peat mining, near inhabited areas. We evaluated the faunal and vegetation patterns after restoration of a peatland formerly mined for peat. We assessed whether bog pools created during restoration are similar to natural bog pools in terms of water chemistry, vegetation structure and composition, as well as amphibian and arthropod occurrence patterns. 2. Both avian species richness and peatland vegetation cover at the site increased following restoration. Within bog pools, however, the vegetation composition differed between natural and man‐made pools. The cover of low shrubs, Sphagnum moss, submerged, emergent and floating vegetation in man‐made pools was lower than in natural pools, whereas pH was higher than in typical bog pools. Dominant plant species also differed between man‐made and natural pools. 3. Amphibian tadpoles, juveniles and adults occurred more often in man‐made pools than natural bog pools. Although some arthropods, including Coleoptera bog specialists, readily colonised the pools, their abundance was two to 26 times lower than in natural bog pools. Plant introduction in bog pools, at the stocking densities we applied, had no effect on the occurrence of most groups. 4. We conclude that our restoration efforts were partially successful. Peatland‐wide vegetation patterns following restoration mimicked those of natural peatlands, but 4 years were not sufficient for man‐made pools to fully emulate the characteristics of natural bog pools.     

Genetic relatedness assessment through individual odour similarities in mice

Previous research has demonstrated that closer genetic relatedness between individuals (from kin to across species) is associated with greater similarity in the qualities of their individual odours ('odour-genes covariance'). This predictable relationship between individual genotypes and individual odours could enable animals to assess their degree of genetic relatedness to other individuals by comparing the degree of similarity between another individual's odour and their own odour. In two-choice tests with odours of unfamiliar mice from different populations and species, subjects from two species of wild mice, Mus spicilegus and M. musculus , that had been raised in mixed litters of both species spent significantly more time investigating the ano-genital odour of the more genetically similar individual. This differential interest was not affected by common rearing with heterospecifics. These responses are consistent with a self-referencing mechanism enabling differential responses across a wide spectrum of genetic relatedness from kin through populations to heterospecifics. These assessments depend on the degree of similarity between the donor's and the subject's odours rather than on differences between them. Such a parsimonious mechanism may provide a basis for differential responses to conspecifics as opposed to heterospecifics that may function as a premating isolating mechanism.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 595–603.     

Does the M-Phase Promoting Factor (MPF) Activate a Major Ca2+-and Cyclic Nucleotide-Independent Protein Kinase in Starfish Ocytes?

In starfish, the activity of a major Ca²⁺-and cyclic nuleotide-independent protein kinase has been shown to fluctuate in phase with that of MPF along meiotic and mitotic cell cycle (23, 25). Microinjection of α-naphthylphosphate (α-NP), a potent phosphatase inhibitor, increased considerably (from 15 to 546 picomoles/min/mg protein) the activity of this major cycling kinase in homogenates. Although this result supported the view that kinase phosphorylation might induce its own activation, this hypothesis was eliminated because injection of cytoplasm from hormone-stimulated enucleated oocytes, which contained the fully activated kinase but no MPF, failed to trigger kinase activation in recipient oocytes. In contrast, kinase activation was induced in recipient oocytes injected with either cytoplasm taken from nucleated maturing oocytes, which contained high MPF and kinase activities, or cytoplasm taken later from hormone-stimulated and ATP-γ-S-injected oocytes which contained high MPF but low kinase activites. These results indicate that inhibiting dephosphorylation of some regulatory protein activates the M-phase-specific protein kinase. The possibility that the M-phase or maturation-promoting factor (MPF) might be this regulatory protein is discussed.     

Observations with Hoechst Staining of Amitosis in Acanthamoeba castellanii

DNA staining with Hoechst 33258 allows us to visualize and to characterize amitotic division of Acanthamoeba castellanii in which the cell nucleus divides without DNA condensation and regular segregation of chromosomes. Amitosis involves several programmed and coordinated steps that exclude accidental cutting of the cell nucleus.     

Reversal of eutrophication in Lake Geneva: evidence from the oligochaete communities

1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m^?3 in 1979 to 55 mg m^?3 in 1990. 2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m. 3. Abundance of mesotrophic species (mostly Potamothrix vejdovskyi) and of eutrophic species (mostly Potamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostly Peloscolex velutinus) were more abundant in 1991 than in 1982. 4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation. 5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1991.     

A Membrane Receptor Mechanism for Steroid Hormones Reinitiating Meiosis in Xenopus Laevis Oocytes*

There is a membrane progesterone receptor in Xenopus laevis oocytes that undergo meiosis under steroid exposure. Early responses include a decrease of leucine uptake, a decrease of adenylate cyclase and alkaline phosphatase activities, and a decrease of the phosphorylation of a specific p48 protein in the membrane. These results are compatible with a decrease of membrane fluidity brought about by the hormonal message. However the above-cited effects as well as the Ca₂₊-changes are not yet enough well understood to be able to precisely delineate their role in meiosis reinitiation.     

Identification of sibling mice species (genus Mus) by a simple immunological test

An immunological test that can be made on living animals is developed to identify M. m. musculus mice from the two other short-tailed mice ( M. spicilegus and M. spretoides ) occurring in Eastern Europe. This test uses fractionated albumin antiserum as an immunological marker and is performed using dot-blot immunoassay. One hundred and twelve animals belonging to the three species and originating from wild-caught mice and from laboratory strains were tested. All the M. m. musculus mice were correctly identified with this test. Owing to its simplicity and reliability, this test will be very useful in field surveys, particularly in the zone of sympatry between M. m. musculus and M. spicilegus .     

Effect of Far Red and Red Light on a Pelletable Peroxidase Activity in Extracts from Spinach Leaves

The effect of in vitro irradiations on ihe pelletability of peroxitlase activity was tested in extracts prepared from leaves of light-grown spinach (Spinacia oleracea). It appeared that far red light increased the pelletable activity and that red light reversed this effect. This phytochrome-mediated effect occurred in a particulate fraction which banded at 39% (w/w) sucrose on an isopycnic density gradient.